Air pressure driven vacuum sewer system

Abstract: A vacuum sewer system comprising a waste receiving unit (1) to be emptied provided with an outlet opening (2) and having a normally closed sewer valve (3) and an ejector (5). The ejector (5) is an integrated part of a sewer pipe (4, 7) connected to the waste receiving unit (1). The sewer pipe includes an upstream portion forming a suction pipe (4) of the ejector (5) and a downstream portion forming a discharge pipe (7) of the ejector (5).

Description: The invention relates to a vacuum sewer system according to the preamble of claim 1. The invention also relates to a transport vehicle incorporating such a vacuum sewer system. In a vacuum system, the sewer pipe must be kept under partial vacuum to enable the waste transport, typical of a vacuum sewer system, to be accomplished. On the other hand, it is convenient to keep the sewage collecting container at atmospheric pressure, because this allows the container to be made less strong and facilitates the emptying thereof. The known solutions for achieving this are, however, relatively complicated and expensive. See, for instance, US-A-3629099, US-A-4184506 and US-A-4034421. The object of the invention is to simplify the equipment required in a vacuum sewer system in which the sewage collecting container is kept at atmospheric pressure. According to the invention this object is achieved by a vacuum sewer system as claimed in the ensuing claim 1. The invention is based on the principle that the required partial vacuum in the sewer pipe is generated by means of a pressurised gaseous working medium driven ejector arranged as an integrated part of the sewer pipe itself. The working medium is preferably air, but the ejector could be driven by other pressurised gases or gas mixtures. The ejector is integrated into the sewer pipe and is preferably located relatively close to any waste receiving unit to be emptied into the vacuum sewer to facilitate servicing or repair of the ejector. A typical such waste receiving unit is a toilet bowl. The invention makes it possible to considerably reduce the amount of energy that is required on each occasion that a toilet bowl or the like is emptied. At the same time, the number of parts required in the system is reduced to a minimum. It is previously known to use ejectors as a source of partial vacuum in vacuum sewer systems. For example, US-A-4034421 shows a system with a liquid driven ejector at the downstream end of the sewer, which ejector generates the partial vacuum necessary for sewage transport. However, this known arrangement is expensive because a separate circulation pump must be used to drive the ejector. Besides, the efficiency rate of the vacuum generation is low, typically only about 5%. Furthermore, the working medium of the ejector is unpurified sewage liquid, which sets special demands, e.g. with regard to the cleaning, etc., on the circulation pump and on the ejector. Also, US-A-4791688 shows a similar system where, in addition, there is employed an extra external air supply for ensuring sewage transport. Other known vacuum sewer systems which use ejectors as sources of partial vacuum are disclosed in WO-A-92/18713 (cf. preamble of claim 1) and FR-A-2637304. The invention is considerably simpler than known systems. Because air is used as the preferred gaseous working medium of the ejector, the invention is particularly suitable for use in trains or other passenger transport vehicles having a pressurised air system which, although primarily serving other purposes, can be used as a driving system for a vacuum sewer arrangement according to the invention. In such a case, the invention does not require the cost of providing an additional air pressure system, since the capacity of such other air systems are usually well sufficient for the limited use required by a vacuum sewer system according to the invention. If, for some reason, it is more convenient to use some gas or gas mixture other than air as the working medium in the ejector, this can be done within the general scope of the invention. In use of the invention, there is a risk that a temporary stoppage or slowing down will occur in the sewage transport downstream of the ejector. In this case, the operation of the ejector will rapidly increase the pressure in the sewer pipe and this pressure may propagate to any toilet bowl, or other waste receiving unit, connected during flushing to the sewer, which would create an undesired pressure surge in the wrong direction in the toilet. Security devices eliminating this risk may be arranged between the toilet bowl and the ejector. If the pressure between the ejector and the toilet bowl when the sewer valve is open rises higher than the pressure in the toilet bowl, the security devices will rapidly close down the ejector or by some other means reduce or eliminate the pressure rise. The security devices may comprise a pressure-sensitive relief valve as well as a pressure sensor connected to the driving system of the ejector. In this way the highest security is obtained, because a closing down of the ejector as well as reduction of the pressure can be obtained simultaneously. A simple but reliable and effective relief valve may comprise a flexible hose, which is connected to the sewer pipe and is normally kept in a bent position so that a closing fold is formed in the hose. The hose should have the possibility of taking, under the influence of internal pressure, a straighter position, in which the fold opens and forms a through-flow duct. When partial vacuum prevails in the sewer pipe, the closing fold of the hose works as a non-return valve since the outer atmospheric pressure closes the fold of the hose, so that it forms a totally tight closure. For any out-flow via the hose a tube duct is arranged, which, for instance, is connected to the sewage collecting container of the system. In a system according to the invention having optimum characteristics, it is sufficient that the ejector is fed with pressurised air for, at the most, a few seconds. At a dynamic pressure in the pressure air network of about 5 bar gauge pressure, less than 5 seconds air delivery is normally required to empty a toilet bowl. Thereby, the pressure in the upstream portion of the sewer pipe, between the sewer valve and the ejector, is reduced by about 25 to 45%, which is quite sufficient for obtaining an effective emptying of a toilet bowl. The amount of air supplied to the ejector is normally in the order of magnitude of 1000 litres/minute, the volume of air being calculated at standard temperature and pressure, that is at normal atmospheric pressure and at a temperature of 0°C. It is of course of advantage to reduce the amount of air fed to the ejector as much as possible, without thereby taking any risks with respects to the secure functioning of the system, since the smaller the consumption of air, the smaller is the energy consumption. The energy consumption of an emptying cycle is also influenced by the volume of the space that is to be set under partial vacuum. The smaller this volume, the smaller is the energy consumption. The upstream portion of the sewer pipe which is set under partial vacuum must not, however, be too short, since the vacuum volume will then be too small to obtain effective emptying of a toilet bowl or other waste receiving unit. It is recommended that the length of the upstream portion of the sewer pipe between the sewer valve and the ejector is from 1 to 5 m, preferably from 2 to 3 m. The function of the pressurised gas, e.g. air, driven ejector may additionally be enhanced by providing the downstream portion of the sewer pipe which forms the discharge pipe of the ejector, within the section where the ejector produces a considerable partial vacuum, with an inner flexible sleeve member forming between its external surface and the sewer pipe a space sealed towards the interior of the sewer pipe. This space should be in connection with the atmosphere surrounding the sewer pipe. During operation of the ejector, a sleeve member arranged in this manner will be contracted, by the flow forces and by the pressure of the ambient atmosphere, to a diameter that is considerably smaller than the diameter of the sewer pipe. Thus the sleeve member provides a narrow duct in the vacuum generating phase, but forms no obstacle when waste or the like has to pass through. Such a flexible sleeve member essentially improves the effect of the ejector, and the amount of pressurised air used may then be reduced, in many cases by up to 2 /3. The sleeve member may have a length of only about 10 cm. It is preferably mounted immediately downstream of the section where the suction pipe of the ejector joins the discharge pipe of the ejector. For obtaining the best action, it is suitable that the upstream part of the sleeve member is provided with a number of axially orientated stiffeners providing a guiding effect on the contracting motion of the sleeve member, especially in its starting phase. The contraction of a suitably devised rubber sleeve member with a wall thickness of about 1 mm and a length of 110 mm, which as described is mounted in a sewer pipe with a bore diameter of 54 mm, may result in the free opening in the centre of the sleeve member having a diameter of only about 10 mm. The ejector may be devised in a number of different ways. One arrangement, usual in ejectors, is for the suction pipe to join the discharge pipe at an angle. It is then suitable that the upstream and downstream portion of the sewer pipe which are connected to the ejector together form an angle of at least 120°, preferably at least 135°. At smaller angles there is a greater risk for disturbances in the flow of sewage through the sewer pipe. It is also feasible for the upstream and downstream portions of the sewer pipe to be aligned so that the sewer pipe runs mainly or substantially linearly through the ejector and for the working medium of the ejector to be supplied either through nozzles arranged circumferentially in the sewer pipe, or though a nozzle which, from the exterior of the sewer pipe, extends through the pipe wall into the interior of the sewer pipe. In this last-mentioned case, it is important for the nozzle member to be provided with such diverting surfaces that the risk of sewage matter getting caught by the nozzle member or by its attachment members is practically eliminated. The vacuum sewer system may include more than one waste receiving unit, although there should not be too many such units so as to keep the consumption of pressurised air (or other gas) to a reasonable level. Embodiments of the invention will now be described, by way of example only, with particular reference to the accompanying drawings, in which: Figure 1 schematically shows a vacuum sewer arrangement according to the invention; Figure 2 schematically shows a section of a relief valve for an arrangement according to the invention; Figure 3 schematically shows an axial section of an ejector according to the invention; Figure 4 shows a side view of a rubber sleeve member being part of the ejector shown in Figure 3; Figure 5 schematically shows an end view of the rubber sleeve member according to Figure 4, in a contracted position; Figures 6 and 7 schematically show ejectors of other embodiments than the ejector shown in Figures 1 and 3; and Figure 8 shows an example of a time chart for the different functions of a vacuum sewer system according to the invention. In the drawings, reference numeral 1 indicates a toilet bowl having an outlet 2 normally closed by a disc valve 3 which may be of the type described in US-A-4713847. The upstream end of a vacuum sewer comprises an upstream portion 4 of a sewer pipe which is directly connected to the disc valve 3. To empty the toilet bowl 1, a partial vacuum is generated in the vacuum sewer by a pressurised air ejector 5, which forms an integrated part of the sewer pipe. Downstream of the ejector 5, a downstream portion 7 of the sewer pipe leads to a sewage collecting container 6. The downstream sewer pipe portion 7 situated between the ejector 5 and the collecting container 6 does not form a vacuum sewer, because it is at the pressure side of the ejector 5. Also the collecting container 6 is outside the vacuum system and is consequently under atmospheric pressure. In order to empty the toilet bowl 1, a user operates a push button 8, or some other suitable device, transmitting an electric signal to a control centre 9, which controls all the functions of the arrangement. On operation of the push button 8, the control centre 9 opens a remote-controlled air feed valve 10 connected to the ejector 5, whereby pressurised air from a pipe 11 of a pressure air system rushes into the ejector. The pressurised air operates as a working medium of the ejector and generates in a very short time a considerable partial vacuum in the ejector and in the upstream portion 4 of the sewer pipe. After about 2.5 seconds the desired vacuum level, that is a pressure reduction of about 40%, is obtained in the sewer pipe portion 4. The disc valve 3 is then rapidly opened, and the ambient atmospheric pressure instantaneously causes the contents of the toilet bowl 1 to be pushed into the upstream portion of the sewer pipe. The ejector 5 is then still in operation and maintains partial vacuum downstream of a plug of sewage that moves very rapidly from the toilet bowl 1 through the upstream sewer pipe portion 4. Simultaneously, the ejector 5 blows the downstream portion 7 of the sewer pipe clean of any liquid or impurity possibly present there. In the embodiment shown, the distance L between the disc valve 3 and the ejector 5 is about 2.3 m. The downstream portion 7 is typically of considerable length (i.e. several metres) so that the ejector 5 is positioned between the ends of, and not at one or the other end of, the combined sewer pipe extending from the disc valve 3 to the container 6 and formed of the sewer pipe portions 4 and 7. The system works well even if the ejector is positioned relatively close to the collecting container 6. However, for service and/or repair of the ejector 5 it is preferred that the ejector is positioned relatively close to the toilet bowl 1. To protect the system from undesirable pressure surges, the vacuum sewer pipe is provided with a relief valve 13 and with a pressure sensor 17 connected to the control centre 9. On detecting a rise of pressure in the sewer pipe portion 4, the pressure sensor 17 rapidly closes the valve 10 thereby stopping further air delivery to the ejector 5. When the ejector 5 is in operation and the valve 3 is opened, the toilet bowl 1 is also supplied with a desired amount of rinse liquid in a manner that cleans the inner surface of the toilet bowl. This function is not described in detail, because it is well known in the art and does not per se have any influence on the application of the invention. As explained in more detail with reference to Figure 8, the ejector is normally closed about 0.5 seconds after the opening of the valve 3. In this time the sewage reaches and passes the ejector 5. Because the sewage is driven forwards by the ambient atmospheric pressure, it is important that the valve 3 is kept open a sufficient length of time, usually about 3 seconds, that a sufficiently large amount of air flows, via the outlet 2 of the toilet bowl, into the upstream portion 4 of the sewer pipe. When the valve 3, upon emptying of the toilet bowl 1, is again closed, the control centre 9 keeps it closed for about at least 5 seconds to ensure that all the sewage reaches the collecting container 6 before the next flush is carried out. In Figure 2, a simple relief valve in the form of a flexible hose 12 is schematically shown. The hose 12 is surrounded by a protective tube 13 and is bent about 90° so that a fold 14 is formed in the hose. The interior of the hose 12 is connected via an aperture 15 to the interior of the vacuum sewer pipe portion 4. The fold 14 totally closes the hose 12, especially when the pressure outside the hose is higher than in the interior of the vacuum sewer pipe portion 4, but also when there is little or no pressure difference between outside the hose and the interior of the vacuum sewer pipe because of the weight of the free end portion of the hose (to the right of the fold 14 in Figure 2). If overpressure occurs in the upstream portion 4 of the sewer pipe, the hose 12 is under the influence of this pressure and is then somewhat straightened to adopt the position 12a shown in dashed lines in Figure 2. In this position 12a, an aperture 14a is opened up at the point where the hose is normally closed by the fold 14. The overpressure can then discharge through the aperture 14a. The protective tube 13 has a continuation not shown in Figure 2. This continuation 13a connects in a suitable manner the relief valve to the downstream portion 7 of the sewer pipe downstream of the ejector, as schematically shown in Figure 1, or directly to the collecting container 6, in both cases in a manner that allows gravity induced flow. Figure 3 schematically shows a preferred embodiment of an ejector according to the invention. The vacuum sewer pipe portion 4 forms an angle of 135° relative to the portion 7 of the sewer pipe downstream of the ejector 5. In the embodiment shown the vacuum sewer pipe portion 4 is mainly horizontal and the sewer pipe portion 7 is inclined downwards in the flow direction. It is also feasible for the sewer pipe portions 4 and 7 to be substantially parallel, but at different levels and/or in different vertical planes, whereby the sewer pipe portion 4 just upstream of the ejector 5 is bent about 45° for its connection to the ejector. However, the embodiment shown in Figure 3 has proved to be the best with respect to operational reliability. The working gaseous medium, preferably air, of the ejector 5 is introduced into the ejector through the pipe 11 at a dynamic pressure of about 5 bar gauge pressure. It is introduced through an aperture of about 3mm in diameter at the end of the pipe 11 into the ejector 5 and flows mainly in the longitudinal direction of the downstream sewer pipe portion 7. Immediately downstream of the pipe 11, the ejector function generates a considerable vacuum within a zone of a length of some tens of centimetres. About in the middle, in the longitudinal direction, of this zone there is a flexible rubber sleeve member or sleeve 18. Between the external surface of the sleeve 18 and the surrounding pipe wall 16, a pressure chamber is formed which is in connection, via an aperture 19, with the atmosphere. Because the sleeve 18 is bent over or double-bent at its downstream end, as shown in Figures 3 and 4, it has a relatively large freedom of motion. The vacuum generated by the ejector 5 in cooperation with the atmospheric pressure, which through the aperture 19 influences the sleeve 18, causes the sleeve to contract by forming folds as schematically shown in Figure 5. The free opening 20 in the centre of the contracted sleeve has a diameter of only about 10 mm. The contracting function of the sleeve has a very advantageous influence on the effectiveness of the ejector 5 and strongly contributes to reducing the air consumption of the ejector. When sewage passes through the sleeve 18, the folded sleeve expands so that larger solid ingredients are also able to pass without difficulty through the sleeve. As apparent from Figure 4, the sleeve 18 has, at its inlet end, an annular stiffener 21, from which four circumferentially spaced-apart, axially extending stiffeners 22 extend to almost the longitudinal middle portion of the sleeve in its double-bent position. The stiffeners 22 cause the sleeve 18 to contract in a desired manner, so that regular folds according to Figure 5 are obtained. Figure 5 shows the sleeve 18 seen from its downstream end. The wall thickness of the sleeve 18 is about 1 mm, at the stiffeners 21 and 22 about twice as much. In the embodiment according to Figure 3, the pipe portion 7, downstream of the ejector 5, is about 40% larger in diameter than the vacuum sewer pipe portion 4 upstream of the ejector. This reduces the risk of flow stoppage or too slow flow in the downstream portion 7 of the sewer pipe. Typically the sleeve has a length of about 110 mm and the pipe wall 16 has a bore diameter of about 54 mm. Figure 6 shows an ejector 5a which is intended for an embodiment where the upstream vacuum sewer pipe portion 4 and the downstream sewer pipe portion 7 are in linear configuration relative to each other. The working medium of the ejector is provided through a pipe 11a which, from the outside, extends mainly at right angles through the wall of the ejector housing 5a up to the centre thereof. To prevent solids, in particular fibrous ingredients, in the sewage from being caught by the pipe 11a, the pipe 11a is provided, at its upstream side, with a deflector plate or the like 23, the upper edge 23a of which is inclined at an angle of preferably at the most 30° from the internal surface of the ejector housing to the top of the pipe 11a. Immediately downstream of the feed pipe 11a, the ejector 5a has a tapered contracting flow duct portion 24 followed by an expanding portion 25, which are formed in the manner that is conventional in ejectors. In the ejector shown in Figure 3, tapered pipe portions such as 24 and 25 are not needed, because the sleeve 18 provides substantially the same function. Figure 7 shows another ejector 5b also intended for linear sewer pipe mounting. In this embodiment, air is supplied through a supply pipe 11b, shown schematically in Figure 7, to an annular duct 11c, from which the air, via a number of circumferentially arranged feed ducts 11d, is blown almost axially into the through flow pipe of the ejector 5b. Figure 8 schematically shows operational sequences when a toilet bowl 1 in a system according to Figure 1 is emptied. The emptying cycle is started by operating the push button 8 for a short period of time, as indicated by section 8a. The ejector 5 is activated and operates for about 3 seconds, as indicated by section 5c. About half a second before the end of the function phase of the ejector 5, the disc valve 3 is opened and is kept open for about three seconds as indicated by section 3a. The function of the ejector reduces the pressure in the vacuum sewer pipe portion 4 by about 40 kPa, as shown by the curve 4a. When the disc valve 3 opens, the pressure in the pipe portion 4 increases rapidly and, after about one or a few seconds, reaches its original value. After the disc valve 3 has been closed, the system is locked for a time T of about five seconds, to avoid very closely repeated flushes which would cause operational disturbances in the system. In all the embodiments described the ejector, whether driven by air or other gases, is positioned between the ends of the sewer pipe or pipes connecting the disc valve 3 to the collecting container 6. Typically each of the upstream sewer pipe portion 4 and the downstream sewer pipe portion 7 has a length of at least 1 m. More than one toilet bowl, or other waste receiving unit, may be included in a vacuum sewer system according to the invention. Thus the upstream portion of the sewer pipe 4 could be connected to more than one toilet bowl 1 although there should not be too many toilet bowls connected in this manner in order to keep the consumption of pressurised air at a reasonable level. Typically, therefore, a pair of toilet bowls may be connected to an ejector via the same sewer pipe portion. Preferably, however, the emptying of the bowls would be controlled so that emptying of both toilet bowls is not initiated at the same time. The invention is not limited to the embodiments disclosed, but several variations or modifications thereof are feasible, including variations which have features equivalent to, but not necessarily literally within the meaning of, features in any of the appended claims.

Claims: A vacuum sewer system comprising a waste receiving unit (1) to be emptied from time to time through an outlet opening (2) thereof, a normally closed sewer valve (3) for controlling the flow of waste from the waste receiving unit through said outlet opening (2), a sewage collecting chamber (6), a sewer pipe having an upstream portion (4) connected to the sewer valve (3) and a downstream portion (7) connected to the sewage collecting chamber (6), an ejector (5) having a suction pipe, a discharge pipe and a working medium supply inlet (11), and means (9) for controlling the operation of the ejector (5) to create a considerable partial vacuum in the upstream portion (4) of the sewer pipe before the sewer valve (3) is opened, characterised in that the ejector is a gas-driven ejector (5) integrated into the sewer pipe (4, 7) as a through-flow element so that the upstream portion (4) of the sewer pipe provides said suction pipe of the ejector and the downstream portion (7) of the sewer pipe provides said discharge pipe of the ejector, sewage being transported, in a transport cycle, as a continuous flour, the sewage firstly being transported in said upstream portion (4) of the sewer pipe, due to pressure difference between the ambient atmosphere and partial vacuum created by the ejector (5), thereafter passing through the ejector and thereafter, in said downstream portion (7) of the sewer pipe, being transported or being assisted by pneumatic pressure created by the ejector (5) in said discharge pipe. A system according to claim 1, characterised in that between the waste receiving unit (1) to be emptied and the ejector (5) there are security devices (13, 17) which are arranged to rapidly close down the ejector (5) and/or reduce the pressure rise in another manner if the pressure between the ejector (5) and the waste receiving unit (1) rises higher than the pressure in the waste receiving unit (1) when the sewer valve (3) is open. A system according to claim 2, characterised in that the security devices include a relief valve in the form of a flexible hose (12) which is normally in a bent position in which a closing fold (14) is formed in the hose. A system according to any of the preceding claims, characterised in that a driving system of the ejector is arranged to feed the ejector (5) with pressurised air for a few seconds at a flow rate in the order of magnitude of 1000 l/min at standard temperature and pressure. A system according to any of the preceding claims, characterised in that the upstream and downstream portions (4, 7) of the sewer pipe are connected to the ejector (5) at an angle and form with each other an angle of at least 120°, preferably at least 135°. A system according to any of the preceding claims, characterised in that the upstream and downstream portions (4, 7) of the sewer pipe run mainly linearly through the ejector (5) and in that the working medium of the ejector is arranged to be introduced into the sewer pipe at circumferentially spaced locations (11d) of, or through a nozzle (11a) extending from the outside through, a wall of the sewer pipe. A system according to any of the preceding claims, characterised in that the length (L) of the upstream portion (4) of the sewer pipe between the sewer valve (3) and the ejector (5) is from 1 to 5 m, preferably from 2 to 3 m. A system according to any of the preceding claims, characterised in that the downstream portion (7) of the sewer pipe which forms the discharge pipe of the ejector, within a zone (16) where the function of the ejector causes a considerable vacuum, comprises an internal flexible sleeve member (18), which between its external surface and the wall of a surrounding pipe (16) forms a space sealed against the interior of the sewer pipe, which space is in connection with the ambient atmosphere, so that the sleeve member (18), when the ejector (5) operates, contracts under the influence of flow forces and the ambient atmospheric pressure to a diameter that is considerably smaller than the diameter of the sewer pipe (4). A system according to claim 8, characterised in that the sleeve member (18) is mounted immediately downstream of the section where the suction pipe of the ejector joins the discharge pipe of the ejector and has a length in its mounted position of about 10 cm. A system according to claims 8 or 9 , characterised in that an upstream part of the sleeve member (18) is provided with a number of stiffeners (21, 22). A passenger transport vehicle comprising a compressed gas, e.g. air, system, characterised in that the vehicle includes a vacuum sewer system according to any one of the preceding claims and in that the compressed gas system is connected to the said working medium supply inlet via valve means for controlling the supply of compressed gas to the ejector.

Inventors: TOERNQVIST HANS, TOERNQVIST, HANS, Törnqvist, Hans
Applicants: EVAC AB
Application year: 1994
Main classification: E03F1
IPC codes: E03F1, E03F7, E03D5, B60R15